In bge, how would I zoom using mouse scroll in ortho view?
Typo on the line 18
positive:: to positive:
You need 2 sensors for each of detect wheel up and down.
And the sensors have to be connected to the python controller.
This is why you got only one of zoom out or in.
You have to make the names in blender to be consistent with the names in the script, also the script file name.


Advice:
You can open console from menu Window &gt; Toggle System Console. The console shows error messages from BGE when BGE is running.
Be carful, closing the console window closes whole blender.